A next generation multimedia wireless communication system that has been actively researched is required to process not only voices but also images, packet data and the like.
Location based services such as an emergency rescue service or a child monitoring service are one of next generation services. However, unsecured location based services may be vulnerable to an unauthorized access that steals location information of a mobile station (MS). If the location information of the MS is exposed, the location information may be used for unauthorized access and undesired exploitation. Accordingly, it is essential to protect privacy of location information of the MS in a wireless communication system. Capability of protecting the location information of the MS against unknown exploiters is called as location privacy.
Orthogonal frequency division multiplexing (OFDM) is a multi-carrier modulation technique using a plurality of orthogonal subcarriers. Orthogonal frequency division multiple access (OFDMA) is a technique for providing multiplexing of multi-users by combining the OFDM with frequency division multiple access (FDMA) or time division multiple access (TDMA).
IEEE (Institute of Electrical and Electronics Engineers) 802.16 standard is based on the OFDM/OFDMA. In the IEEE 802.16 standard, ranging is a collection of processes by which a MS and a BS maintain the quality of the RF communication link between them. The ranging consists of two types: initial ranging and periodic ranging. The first serves to initiate registration (or re-registration) of a MS with a base station (BS). The second served to periodically readjust physical parameters of the MS and to verify that the MS is still on line. The initial ranging is needed for a procedure in which the MS registers with the BS or a handover.
Hereinafter, downlink indicates communication from the BS to the MS, and uplink indicates communication from the MS to the BS.
Initial ranging is the procedure to obtain an accurate timing offset between the MS and the BS and to adjust transmission power. When a MS is turned on, the MS achieves downlink synchronization from downlink preambles. Subsequently, the MS performs the initial ranging so as to adjust uplink timing offset and transmission power. After the initial ranging is completed, periodic ranging is periodically performed to track uplink timing offset and received signal strength.
In general, after initial ranging is completed, authentication between the MS and the network is performed to allocate a message authentication code. The message authentication code is used to protect messages which are exchanged between a MS and a BS from being exposed to another MS. However, a method of protecting location privacy before the authentication between the MS and the network is completed is not disclosed.
A method is sought of preventing the location information of the user from being exposed before the authentication between the MS and the network is completed.